(i) Technical Field
The present invention relates to adhesives for adhesive layers of fixing members, fixing members, fixing devices, and image-forming apparatuses.
(ii) Related Art
Electrophotographic image-forming apparatuses, such as copiers and printers, form an image on a recording medium such as recording paper by fixing an unfixed toner image using a fixing device. Examples of fixing devices for use in such image-forming apparatuses include roller-to-roller fixing devices and belt-nip fixing devices. A roller-to-roller fixing device includes a thermal fixing roller serving as a fixing member and a pressing roller serving as a pressing member. A belt-nip fixing device, which is a technology for achieving, for example, faster image-forming apparatuses, includes a rotatable fixing roller serving as a fixing member, a belt member movable in contact with the fixing roller, and a non-rotatable pressure pad serving as a pressing member inside the belt member. The surface of the fixing roller is elastically deformable. The pressure pad presses the belt member against the fixing roller to form a contact area with the fixing roller, thereby forming a nip through which a recording medium passes between the belt member and the fixing roller.
Elastic rollers are used as fixing rollers in fixing devices, particularly for color applications. Elastic rollers are often made of silicone rubbers, which are a type of heat-resistant rubber. Recently, many elastic rollers have been proposed that are covered with a tube such as a fluoropolymer tube as a surface layer. This surface layer serves as a toner release layer to improve compatibility with toners for oil-free fixing, which, unlike conventional toners, contain wax so that no oil has to be used to assist in toner release.
An example method for manufacturing an elastic roller covered with a fluoropolymer tube is one-piece molding, which involves molding a layer of fluoropolymer formed in a tubular shape in advance and an elastic layer containing a rubber material in a single mold to bond them together. Another method involves forming and vulcanizing an elastic layer and then covering the elastic layer with a fluoropolymer tube. Yet another method involves coating an elastic layer with a fluoropolymer dispersion, for example, by spraying or dipping, and then baking the coating. Tubes are often used, for example, for reasons of wear resistance. In this case, for example, an adhesive composition is applied to the elastic layer before the elastic layer is covered with the tube to obtain a fixing roller.
When subjected to a heat aging test that simulates the conditions where a fixing roller is used in an image-forming apparatus, a fixing roller manufactured by one-piece molding may undergo cohesive failure in the elastic layer. A fixing roller manufactured by covering an elastic layer with a tube in a later step includes an adhesive layer that bonds together the elastic layer and the surface layer; however, it may have insufficient adhesion strength because of separation between the layers or the insufficient strength of the adhesive layer itself.